Calcium oxide-chromium oxide refractory



Patented Feb. 11, 1941 UNITED STATES CALCIUM OXIDE-CHROMIUM oxm'nREFRACTQRY' Gordon R. Pole, ncar;Sheffield, Ala.

No Drawing. Application November 21, 1938,

Serial No. 241,635

3 Claims.

(Granted under the act or March a, 1883, as amended April 30, 1928; 3700. G. 757) The invention herein described may be manufactured and usedby or for the Government for governmental purposes without the paymentto me of any royalty thereon.

5'. This invention relates to the art of making highly refractorycompositions and articles of manufacture.

The principal object of this inventionis to produce a high melting pointrefractory which will withstand the corrosive action of basic slags andother basic melts, such as fused rock phosphate. Another object of thisinvention is to produce a chromium oxide refractory with physical andchemical characteristics such that the structure of the refractory willnot be materially affected by repeated treatment at high temperatures.Still another object of this invention is to provide a chromium oxiderefractory which is also stable in the presence of water vapor atrelatively low temperatures. Other objects of this invention include theprovision of a rapid and relatively economical procedure for theproduction of a stable refractory from commercial chromium oxidesuitable for use at relatively high temperatures.

I have discovered a new high melting point refractory, and articles ofmanufacture produced from the same, made by firing a mixture ofsubstantial proportions of calcium oxide and chromium oxide withproportions such that the composition is characterized by its resistanceto hydration in air or in boiling water and its resistance to fusedbasic materials, such as rock phosphate, at temperatures of the order of1500 to 1550 C. The preferred composition contains calcium oxide andchromium oxide in substantially equal proportions.

One example for the production of highly refractory material accordingto my invention is given for the production of highly refractorycrucibles. A mixture of 30 percent by weight mol percent) of calciumoxide of approximately 200 mesh and 70 percent by Weight (50 molpercent) of chromium oxide of approximately 200 mesh, was dry-pressed incrucible forms and the pressed mixture fired to 1605" C. The cruciblesresulting therefrom were found to be resistant to hydration both in airand in boiling water.

50 Rock phosphate charged to the crucibles was fused, the melt pouredand the process repeated with nine separate charges at temperaturesbetween i530 and 1560" C. with the result that the crucibles showed highresistance to corrosion by the fused rock phosphate.

A second example for the production of highly refractory materialaccording to my invention is given for the production of highlyrefractory crucibles with a. modification of the procedure given in theexample above. A mixture of 30 percent by weight (50 mol percent) ofcalcium oxide of approximately 200 mesh and '70 percent by weight (50mol percent) of chromium oxide of approximately 200 mesh, wasdry-pressed into cylindrical shapes and fired to 1605 C. The firedshapes were crushed to a size that would produce a minimum of voids whensubsequently drypressed in crucible forms. The fine refractory materialwas moistened with between 1 percent and 5 percent by Weight of water,dry-pressed -5: into crucible forms and the pressed crucibles fired to1500 to 1605 C. The crucibles showed sub- 'stantially less shrinkagethan those produced according to the first example and they exhibitedthe same resistance to hydration and corrosion 20 by fused rockphosphate.

The procedure used in the preceding examples has been repeated using 23percent by weight of calcium oxide and 77 percent by weight of chromiumoxide (45 mol percent and mol percent 25 respectively) with theproduction of articles which exhibited substantially the samecharacteristics as those indicated in the preceding examples.

It is evident that there are numerous factors 30 which will influenceconditions for the most satisfactory operation of my invention, theactual limits of which cannot be established except by a detailed studyof each set of raw materials and the intermediate and finished productsinvolved. 35

Calcium oxide melts at approximately 2572 C. and chromium oxide melts atapproximately 2300 C. One eutectic mixture of these two materialscontains respectively approximately 30 mol .percent of calcium oxide and'70 mol percent of 40 chromium oxide and another eutectic mixturecontains respectively approximately mol percent of calcium oxide and 25mol percent of chromium oxide. The melting point diagram indicates thepresence of a compound containing 45 approximately 50 mol percentcalcium oxide and 50 mol percent chromium oxide.

I have found that mixtures of calcium oxide and chromium oxide inproportions corresponding in general to the ratio contained in thecompound referred to above, namely, 50 mol percent of both calcium oxideand chromium oxide, produce a refractory which is resistant to hydrationat low temperatures and is resistant to the corrosion of fused basic 55chromium oxide will produce a most satisfactory product. The exactlimits of the ratio of calcium oxide to chromium oxide has not beendefinitely established but as long as the .composition contains a verysubstantial proportion of both calcium oxide and chromium oxide asatisfactory product which will not hydrate in water and which isresistant to the corrosion of fused rock phosphate can be obtained.Calcium oxide may be used directly, but it is preferable to use thecalcium oxide in the form of calcium hydroxide in order to avoidhydration of the former, particularly where dry-pressed unfired articlescontaining calcium oxide may be required to stand in a-moist atmospherefor an appreciable time before firing. Likewise, highgrad-e commercialmaterials are preferred for the production of the refractory madeaccording to my invention for reasons well known in the art.

I have found that raw materials in the propertions indicated may eitherbe fired to approximately 1600 C. to form a highly refractorycomposition, dryepressed in the form of crucibles, shapes or otherarticles of manufacture and fired to approximately 1600 C., or the firedrefractory compositions'may be crushed, dry-pressed into such forms andfired to temperatures of the order of 1500 to 1600 C. The latterprocedure is preferable in the manufacture of large sized refractoriessince the preliminary firing produces a dense body and the use of suchdense body in the production of articles reduces the shrinkage of thelatter during processing to the minimum.

The refractory produced according to my invention is adapted to be usedwhere resistance to high melting point basic melts is required.Throughout the description reference has been made to the resistance ofthis refractory to fused rock phosphate. This index has been used sinceit has been found that fused rock phosphate containing approximatelypercent by weight of calcium oxide one of the most corrosive of fusedbasic materials which may be encountered at temperatures of the order of1500 to 1550 C.

It will be seen, therefore, that this invention actually may be carriedout by the use of various modifications and changes without departingfrom its spirit and scope.

I claim:

1. As an article of manufacture a pressed and fired mixturesubstantially consisting of calcium oxide and chromium oxide inproportions corresponding approximately to a compound containing aboutmol percent of each.

2. A high melting point refractory resistant to corrosion of fused rockphosphate which consists of a fired mixture of 40 to mol percent ofcalcium oxide and 60 to 4.0 mol percent of chromium oxide.

3. A high melting point refractory resistant to corrosion of basicmaterial which consists of a fired mixture of substantially calciumoxide and chromium oxide in proportions corresponding approximately tothe eutectic mixture containing about 50 mol percent each.

GORDON R. POLE.

